The present invention relates to a technology for examining surface defects of a belt-like body to be examined such as a web, that runs continuously.
In order to examine surface defects of a plastic film, a sheet, a thin metal foil, their laminated sheets, or another belt-like body, there are various surface examining apparatuses.
As one of them, there is a surface examining apparatus which irradiates an examinatorial light the surface of a body to be examined (herein after, referred to as xe2x80x9can examined bodyxe2x80x9d) to detect its permitted light or its reflected ii ht by a light receiver and detects photoelectrons. Then, the surface examining apparatus detects the presence of the surface defects by this photoelectric detection outputted. In the surface examining apparatus, a light shielding plate is used in order to prevent the examinatorial light incident directly on the light receiver in error.
Various modes of the light shielding plate are disclosed in JP-UM-A-63-115746. Herein, a light shielding plate is arranged between a projector and an examined body. The examined body is irradiated with a laser beam used as an examinatorial light in such a manner that the laser beam traverses in a width direction of the examined body. The laser beam that is going to travel outward from outer ends in the width direction of the examined body (referred to also as xe2x80x9cedgesxe2x80x9d) is shielded by the light shielding plate. Thus, the laser beam traveling outward from the edges of the examined body is prevented from being incident directly on a light receiver.
In JP-A-04-125455, a surface examining apparatus is disclosed, which can allow a light shielding plate to follow the movement of the edge of an examined body, when the examined body meanders. The examined body is irradiated with a laser beam in the shape of a circular arc (a quarter sector) centered on a projector. A rotary member that comes into contact with the edge of the examined body is coupled to the light shielding plate arranged between the projector and the examined body. While the edge of the examined body does not move in a width direction thereof and the examined body runs normally, the rotary member only rotates and does not move in the width direction. However, when the edge moves in the width direction with meandering of the examined body, the rotary member is moved in the width direction, so that the light shielding plate coupled to the rotary member is also moved in the width direction. According to this technology, the surface examining apparatus can correspond to not only meandering of the examined body but also change in width dimension of the examined body, so that the laser beam that is going to be incident directly on a light receiver can be shielded by the light shielding plate.
In the surface examining apparatus disclosed in the JP-A-04-125455, when the edge of the examined body moved in the width direction, the light shielding plate had a tendency of larger movement than that is desired in the width direction. The edge of the examined body is irradiated slantingly with the laser beam traveling toward the examined body in the shape of the circular arc (a quarter sector) centered on the projector. Generally, the normal running state where the edge of the examined body is not moving in the width direction is assumed, and the position in the width direction of the light shielding plate placed between the projector and the examined body is set so that the edge of the examined body can be irradiated with the laser beam and so that the laser beam traveling outward of the edge can be completely shielded by the light shielding plate.
For example, when the edge moves closer to the center of the examined body than the position in the normal running state with meandering of the examined body (i.e., the width of the examined body along line 50a decreases), the light shielding plate is also moved inward by the same distance. At this time, the laser be is excessively shielded by the light shielding plate, so that the edge of the examined body is not irradiated. Since the light shielding plate is closer to the projector side than the examined body side and the edge of the examined body is irradiated slantingly with the laser beam, in case that the light shielding plate is moved by the same distance as the distance by which the edge has moved, the light shielding plate shields the laser beam excessively. Therefore, the surface examination cannot be performed with a high accuracy.
The present invention has been made in view of the above circumstances, and its object is to provide a surface examining apparatus and a surface examining method in which the light shielding plate can be suitably moved in accordance with the movement of the edge of the examined body.
The object of the invention is achieved by a first aspect of the present invention, there is provided a surface examining apparatus for examining surface defects of a belt-like examined body comprising: a projector irradiating an examinatorial light on the examined body that runs continuously in a Z-direction, and arranged at a distance from a surface of the examined body in a Y-direction orthogonal to the surface of the examined body and arranged inwardly of outer ends of the examined body in the width direction thereof in an X-direction orthogonal to both of the Z-direction and the Y-direction; a light receiver detecting the light that has passed through the examined body; and a light shielding unit including a light shielding member that is arranged between the projector and the examined body and shields the examinatorial light that is going to travel outwards from the outer ends of the examined body in the width direction thereof, and a moving unit that moves the light shielding member in the X-direction and in the Y-direction.
Further, the object of the invention is achieved by a second aspect of the present invention, in which there is provided a surface examining method for examining surface defects of a belt-like examined body comprising steps of: preparing the examined body that runs continuously in a Z-direction; preparing a projector arranged at a distance from the surface of the examined body in a Y-direction orthogonal to the surface of the examined body and arranged inwardly of the outer ends of the examined body in the width direction thereof in an X-direction orthogonal to both of the Z-direction and the Y-direction; preparing a light shielding member arranged between the projector and the examined body; irradiating an examinatorial light from the projector on the examined body; moving the light shielding member in the X-direction and in the Y-direction according to the positional change of the outer end of the examined body in the width direction thereof, thereby to shield the examinatorial light that is going to travel outwards from the outer ends in the width direction of the examined body; and detecting the light that has passed through the examined body by a light receiver.
According to the above structures, the light shielding member can be moved not only in the X-direction which is a direction along the width direction of the examined body but also in the Y-direction which is a direction toward the projector from the examined body. Hereby, the light shielding member can be accurately moved in accordance with the positional change of the edge of the examined body. Therefore, by the light shielding member, the edge is always permitted to be irradiated with the examinatorial light and the examinatorial light traveling outward of the edge can be surely shielded.
In the above constitution, it is preferable that the surface examining apparatus as set forth in the first aspect of the present invention, further comprising a sensor for detecting the position of the outer end of the examined body in the width direction thereof, wherein the moving unit moves the light shielding member on the basis of the state of the sensor.
Further, in the above structure, it is preferable that the moving unit moves a leading end of the light shielding member nearly along a curve drawn by an expression [1],
y=dxc3x97L/(dxe2x88x92x)xe2x80x83xe2x80x83[1]
in which y represents a position in the Y-direction of the leading end of the light shielding member, x represents a position in the X-direction of the leading end of the light shielding member, d represents a distance in the X-direction from the origin to the projector, L represents a distance in the Y-direction from the origin to the leading end of the light shielding member, and the origin of the expression [1] is a position of the outer end of the examined body in the width direction thereof in the normal running state. Further the moving unit moves the leading end of the light shielding member along an approximate straight line or an approximate curve of the curve drawn by the expression [1].
Further, in the above structure, it is preferable that the moving unit further includes a guide having a shape nearly according to the curve drawn by the expression [1], and the light shielding member is moved along the guide.